The XXL Survey

XXX. Characterisation of the XLSSsC N01 supercluster and analysis of the galaxy stellar populations

¹ INAF – Osservatorio astronomico di Padova, Vicolo Osservatorio 5, 35122 Padova, Italy
e-mail: valentina.guglielmo@oapd.inaf.it
² Aix Marseille Univ., CNRS, CNES, LAM, Marseille, France
³ Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany
⁴ School of Physics, University of Melbourne, VIC 3010, Australia
⁵ Instituto de Radioastronomìa y Astrofìsica, UNAM, Campus Morelia, A.P. 3-72, C.P. 58089, Mexico
⁶ INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica Milano, Via Bassini 15, 20133 Milan, Italy
⁷ Departamento de Astronomìa, DCNE-CGT, Universidad de Guanajuato; Callejón de Jalisco, S/N, Col. Valenciana, 36240 Guanajuato, Gto., Mexico
⁸ AIM, CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cité, 91191 Gif-sur-Yvette, France
⁹ INAF – Osservatorio Astronomico di Bologna, via Gobetti 93/3, 40129 Bologna, Italy
¹⁰ Argelander Institut für Astronomie, Universität Bonn, Auf dem Huegel 71, 53121 Bonn, Germany
¹¹ School of Physics, HH Wills Physics Laboratory, Tyndall Avenue, Bristol GB-BS8 1TL, UK
¹² Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Road, Victoria, BC, Canada
¹³ Astrophysics Research Institute, Liverpool John Moores University, IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool GB-L3 5RF, UK
¹⁴ INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00078 Monte Porzio Catone (Rome), Italy
¹⁵ School of Physics and Astronomy, Monash University, Clayton, Victoria 3800, Australia
¹⁶ International Centre for Radio Astronomy Research (ICRAR), The University of Western Australia, M468, 35 Stirling Highway, Crawley, 6009, Australia
¹⁷ SUPA, School of Physics & Astronomy, University of St Andrews, North Haugh, St Andrews GB-KY16 9SS, UK
¹⁸ Dipartimento di Fisica e Astronomia, Alma Mater Studiorum - Università di Bologna, via Gobetti 93/3, 40129 Bologna, Italy
¹⁹ Main Astronomical Observatory, Academy of Sciences of Ukraine, 27 Akademika Zabolotnoho St., 03680 Kyiv, Ukraine
²⁰ Department of Physics and Michigan Center for Theoretical Physics, University of Michigan, Ann Arbor, MI 48109, USA
²¹ ESA/ESTEC, Noordwijk 2201 AZ, The Netherlands
²² Astrophysics and Cosmology Research Unit, University of KwaZulu-Natal, 4041 Durban, South Africa
²³ Australian Astronomical Observatory, PO BOX 915, North Ryde 1670, Australia
²⁴ Department of Space, Earth and Environment, Onsala Space Observatory, Chalmers University of Technology, 439 92 Onsala, Sweden
²⁵ INAF – Osservatorio Astronomico di Brera, via Brera, 28, 20121 Milano, Italy
²⁶ Laboratoire Lagrange, UMR 7293, Université de Nice Sophia Antipolis, CNRS, Observatoire de la Côte d’Azur, 06304 Nice, France
²⁷ Department of Physics and Astronomy, Macquarie University, NSW 2109, Australia and Australian Astronomical Observatory PO Box 915, North Ryde NSW 1670, Australia
²⁸ Department of Astronomy, University of Geneva, ch. d’Ecogia 16, 1290 Versoix, Switzerland
²⁹ Physics Department, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece
³⁰ IAASARS, National Observatory of Athens, 15236 Penteli, Greece
³¹ School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham GB-B15 2TT, UK
³² Ulugh Beg Astronomical Institute of Uzbekistan Academy of Science, 33 Astronomicheskaya str., Tashkent 100052, Uzbekistan
³³ Department of Physics, University of Zagreb, Bijenicka cesta 32, 10000 Zagreb, Croatia

Received: 20 December 2017
Accepted: 18 April 2018

Abstract

Context. Superclusters form from the largest enhancements in the primordial density perturbation field and extend for tens of Mpc, tracing the large-scale structure of the Universe. X-ray detections and systematic characterisations of superclusters and the properties of their galaxies have only been possible in the last few years.

Aims. We characterise XLSSsC N01, a rich supercluster at z ~ 0.3 detected in the XXL Survey, composed of X-ray clusters of different virial masses and X-ray luminosities. As one of the first studies on this topic, we investigate the stellar populations of galaxies in different environments in the supercluster region.

Methods. We study a magnitude-limited (r ≤ 20) and a mass-limited sample (log(M_*∕M_⊙) ≥ 10.8) of galaxies in the virialised region and in the outskirts of 11 XLSSsC N01 clusters, in high-density field regions, and in the low-density field. We compute the stellar population properties of galaxies using spectral energy distribution (SED) and spectral fitting techniques, and study the dependence of star formation rates (SFR), colours, and stellar ages on environment.

Results. For r ≤ 20, the fraction of star-forming/blue galaxies, computed either from the specific-SFR (sSFR) or rest-frame colour, shows depletion within the cluster virial radii, where the number of galaxies with log (sSFR/ yr⁻¹) > −12 and with (g − r)_restframe < 0.6 is lower than in the field. For log(M_*∕M_⊙) ≥ 10.8, no trends with environment emerge, as massive galaxies are mostly already passive in all environments. No differences among low- and high-density field members and cluster members emerge in the sSFR-mass relation in the mass-complete regime. Finally, the luminosity-weighted age–mass relation of the passive populations within cluster virial radii show signatures of recent environmental quenching.

Conclusions. The study of luminous and massive galaxies in this supercluster shows that while environment has a prominent role in determining the fractions of star-forming/blue galaxies, its effects on the star formation activity in star-forming galaxies are negligible.